The compositions and methods of use described herein generally are in the field of materials and methods for enhancing cellular internalization.
It is often difficult to deliver compounds, such as proteins, peptides, genetic material, and other drugs and diagnostic compounds intracellularly because cell membranes often resist the passage of these compounds. Various methods have been developed to administer agents intracellularly. For example, genetic material has been administered into cells in vivo, in vitro, and ex vivo using viral vectors, DNA/lipid complexes, and liposomes. While viral vectors are efficient, questions remain regarding the safety of a live vector and the development of an immune response following repeated administration. Lipid complexes and liposomes appear less effective at transfecting DNA into the nucleus of the cell and potentially may be destroyed by macrophages in vivo.
Proteins and peptides are typically administered by parenteral administration, or, in some cases, across the nasal mucous membrane. Uptake of drugs administered topically is frequently poor, and degradation frequently occurs when drugs are administered orally. For example, hormones such as gonadotropin releasing hormone (“GnRH”) and its analogs have been administered to humans in an attempt to increase fertility by increasing systemic levels of luteinizing hormone (“LH”). When given often, low doses of native GnRH have been shown to induce follicular development and ovulation. These drugs are typically administered via an indwelling catheter into the abdominal cavity. An external pump is attached to the catheter which injects the peptide at frequent intervals. This method of administration is extremely invasive and undesirable. Also, the method is prohibitively expensive for use in animals.
It has recently been demonstrated that, by embedding individual cell populations in hydrogel media of macroscopic viscosity similar to that characteristic of cell cytoskeleta, the rate of receptor-mediated endocytosis can be significantly enhanced (Edwards, et al., Proc. Natl. Acad. Sci. U.S.A. 93:1786-91 (1996); PCT US97/03276 by Massachusetts Institute of Technology and Pennsylvania State University Foundation). This enhancement effect appears to reflect a fluid-mechanical origin of receptor-mediated endocytosis, involving the rapid expansion of plasma membrane in the vicinity of a receptor cluster leading to an invaginating membrane motion that is sensitive to the viscous properties of the extracellular environment (Edwards, et al., Proc. Natl. Acad. Sci. U.S.A. 93:1786-91 (1996); Edwards, et al., Biophys. J. 71:1208-14 (1996)).
It has been found, however, that the delivery of compounds via a receptor-mediated route into the systemic circulation by noninvasively delivering the compound in a “rheologically-optimized” hydrogel may be inconsistent or poorly reproducible. It would be advantageous to better understand the role of RME in uptake of compounds in order to develop improved methods of delivery of compounds, such as drugs, intracellularly.
The binding of ligands or assembly proteins to surface receptors of eucaryotic cell membranes has been extensively studied in an effort to develop better ways to promote or enhance cellular uptake. For example, binding of ligands or proteins has been reported to initiate or accompany a cascade of nonequilibrium phenomena culminating in the cellular invagination of membrane complexes within clathrin-coated vesicles (Goldstein, et al., Ann. Rev. Cell Biol. 1:1-39 (1985); Rodman, et al., Curr. Op. Cell Biol. 2:664-72 (1990); Trowbridge, Curr. Op. Cell Biol. 3:634-41 (1991); Smythe, et al., J. Cell Biol. 108:843-53 (1989); Smythe, et al., J. Cell Biol. 119:1163-71 (1992); and Schmid, Curr. Op. Cell Biol. 5:621-27 (1993)). This process has been referred to as receptor-mediated endocytosis (“RME”). Beyond playing a central role in cellular lipid trafficking (Pagano, Curr. Op. Cell Biol. 2:652-63 (1990)), RME is the primary means by which macromolecules enter eucaryotic cells.
An effective strategy for enhancing the uptake of cytotoxic and therapeutic drugs involves exploiting the rapidity and specificity of transmembrane transport via receptor-mediated endocytosis (Goldstein, et al., Ann. Rev. Cell Biol. 1:1-39 (1985)) by targeting receptors on the plasma membranes of endothelial (Barzu, et al., Biochem. J. 15;238(3):847-854 (1986); Magnusson & Berg, Biochem. J. 257:65-56 (1989)), phagocytic (Wright & Detmers, “Receptor-mediated phagocytosis” in The Lung: Scientific Foundations (Crystal, et al., eds.), pp. 539-49 (Ravens Press, Ltd., New York, N.Y.(1991)); and tumor cells, as well as cells of other tissues. Receptor targeting has, however, not been championed as a means of avoiding intravenous injection of hard-to-absorb macromolecules, probably because macromolecules often degrade prior to reaching receptors in the gastrointestinal tract following oral administration, and do not appear to require receptor-mediation to permeate across the alveolar epithelium following inhalation. Other noninvasive macromolecular drug delivery strategies either do not expose receptors to the topical environment, for example transdermal delivery, or have been less extensively explored, such as nasal delivery (Illum, et al., Int. J. Pharm. 39:189-99 (1987)), vaginal delivery, or ocular delivery.
It is therefore an object of the present invention to provide compositions and methods for enhancing intracellular delivery of bioactive and/or diagnostic agents, especially steroidal compounds and materials which are endocytosed by a receptor-mediated mechanism.